Recently, the demand for processed foods having a meat-like flavor has been increased with westernization and diversification of the eating habits in Japan. Particularly, in the production of soups, processed meat products such as ham, sausage and the like, and cooked foods such as hamburger and the like, there is an increasing demand for good tasting and inexpensive meat flavor.
Heretofore, as a means for imparting meat flavor to foods without using meat itself or for the purpose of general improvement of the flavor or savor of foods is used a sulfur-containing compound such as glutathione, cysteine, glutamylcysteine or the like. For example, it has been already known in, e.g., Japanese Patent Application Laid-Open (Kokai) Nos. 66069/'92, 91762/'92 etc., that food materials obtainable by heating glutathione or γ-glutamylcysteine, or a yeast extract or the like containing glutathione or γ-glutamylcysteine in the presence of a sugar, are effective for enhancing food savor.
In greater detail, the former (Japanese Patent Application Laid-Open (Kokai) No. 66069/'92) describes as follows: “as a result of their extensive studies for obtaining more preferable meat flavor seasonings, the present inventors have found that a roast meat flavor-like seasoning having a good quality and excellent stability without the afore-mentioned unpleasant odor and taste derived from yeast, can be obtained by adding a sugar and an amino acid, if required, to a yeast extract containing a sulfur-containing compound such as glutathione, cysteine, glutamylcysteine or the like in an amount of 2 to 20% by weight (solid content concentration), followed by heating the resulting mixture in the absence of fat” (in the beginning of the “Means for solving the Problems” section of the patent document) and, based on such findings, they have accomplished “a method for producing a seasoning which comprises steps of adding a sugar and an amino acid, if required, to a yeast extract containing a sulfur-containing compound such as glutathione, cysteine, glutamylcysteine or the like in a predetermined amount (2 to 20% by weight of the extract), and heating then the mixture in the absence of fat at 70 to 180° C. for 10 to 180 minutes” (in the “Claims” section of the patent document).
The latter (Japanese Patent Application Laid-Open (Kokai) No. 91762/'92) describes as follows: “a variety of conventional meat flavors have been known, but they are all have a different quality from the aroma of roasted natural meat, and therefore, a flavor imparting agent having a closer quality to roasted natural meat flavor has been wanted.” (in the “Problems to be Solved by the Invention” section of the patent document); and in the situation, “as a result of studies of a flavor of heated and browned various amino acids and sugars for the purpose of solving these problems, the present inventors have found that a flavor composition having a pleasant roasted meat aroma or flavor can be produced by adding a sugar to γ-glutamylcysteine and dissolving the resulting mixture in water, followed by subjecting the solution to a heat reaction by heating at 70 to 180° C. for 10 to 180 minutes, and thus accomplished the present invention” (in the “Means for Solving the problems” section of the patent document). Thus, it discloses “a method for producing a flavor composition comprising the steps of adding a sugar to γ-glutamylcysteine and heating the resulting mixture at 70 to 180° C. for 10 to 180 minutes”.
By either method, however, meat flavor is indeed increased, but problems of a burnt odor, a chemical odor and the like are pointed out.
In addition, there are problems that the seasonings produced by the above methods have an unpleasant, strongly pungent taste owing to cysteine or γ-glutamylcysteine, and the seasonings produced by using glutathione have an unclear taste.
On the other hand, cysteinylglycine is known as one of sulfur-containing compounds. Cysteinylglycine is a dipeptide obtainable by combination of cysteine and glycine through peptide linkage, and is considered to be a possible pleasant meat flavor enhancing material similar to cysteine and glutathione. However, as methods for producing cysteinylglycine, indeed, a peptide synthesis has been known, but a producing method from a natural material has hitherto not been known. In the case that cysteinylglycine is to be used for the above purpose, there is a strong demand for a natural food material containing the same at a high content, but such a natural food material containing cysteinylglycine at a high content has hitherto not been known.